The present invention relates generally to wood processing apparatus, and particularly to a planer producing smooth surfaced high grade dimensioned lumber.
A planer is a crucial portion of a dimensioned lumber manufacturing process. The planer takes rough sawed boards and cuts each surface to provide a smooth, planed final product. Planers operate at tremendous production levels. For example, a typical planer will run on average 1,400 lineal feet of dimensioned lumber per minute. The planer feeds a downstream process including grading, sorting and stacking stations. If the planer goes off line, the entire operation shuts down and production is lost. Thus, maintaining constant, high output by the planer is crucial to overall production.
Because planers operate at such high capacity and with close tolerance relative to board dimensions, boards sometimes become jammed in the planer and require manual removal. Typically, the planer operator must shutdown the planer and physically manipulate the planer, e.g., move vertically a pressure plate opposing a cutter head, to remove jammed or oversized wood articles. As may be appreciated, the operator must quickly resolve any such jams to maintain high production levels. Another source of production loss is the need to dismount cutter heads. While spare cutter head assemblies may be available for mounting, the process of removing supporting shafts, bearing housings, and cutter heads requires time, operator effort, and the assistance of lifting devices, e.g., a crane. Thus, the task of removing a cutter head assembly and mounting a new cutter head assembly can significantly decrease production levels.
Planers often introduce defects into the resulting product due to board instability as it encounters the planer cutter heads. Such defects devalue a given percentage of the production run.
FIG. 1 illustrates schematically a top view of a conventional planer arrangement including a first infeed roller pair 12 and a second infeed roller pair 14. Each roller pair 12 and 14 includes an upper roller and a lower roller, FIG. 1 illustrating only the upper rollers 12a and 14a, it being understood that directly below rollers 12a and 14a are corresponding lower rollers of each roller pair. Roller pairs 12 and 14 capture a board between the upper and lower rollers and propel the board past a top cutter head 16 and a bottom cutter head 18. Cutter head 16 cuts the upper surface of the board as the board bears against an opposing bed plate (not shown in FIG. 1) while slightly downstream cutter head 18 cuts the lower surface of the board as the board bears against an opposing top pressure plate thereabove. Planer 10 further includes downstream a left side cutter head 30 and a right side cutter head 32 planing left and right sides, respectively, of the board passing therebetween.
Thus, a board driven through planer 10 by feed roller pairs 12 and 14 passes by the cutter heads 16, 18, 30, and 32. The rotational direction of roller pairs 12 and 14 define a feed direction 20. To maintain the board stable throughout the planing processing, a guidebar 34 defines the feed path. The board must be maintained stable against the guidebar 34 to achieve a smooth planed surface on all sides of the board and avoid planing defects. Traditional planers maintain the board against the guidebar 34 by providing an angled lead for the board relative to a planer centerline. More particularly, each of the rollers 12 and 14 and the cutter heads 16 and 18 have parallel axes of rotation 36, 38, 40, and 42, respectively. The axes of rotation 36, 38, 40, and 42 are all normal, i.e., ninety degrees, to a planer 10 centerline 44. Force vectors developed by roller pairs 12 and 14 and by cutter heads 16 and 18 and applied to the board are, therefore, parallel to centerline 44. Guidebar 34 lies parallel to an angled datum line 45, with datum line 45 more widely separated from centerline 44 at the infeed portion of planer 10 then at the downstream or outfeed portion of planer 10. The face 34a of guidebar 34 has a given, slight angled relationship relative to the axes of rotation 36 and 38 for feed rollers 12 and 14. The force of movement applied to the board by roller pairs 12 and 14 is, therefore, into the face 34a guidebar 34 rather than parallel to guidebar 34. As a result, board 20 is maintained against guidebar 34 by virtue of the angled lead established between the board and roller pairs 12 and 14.
Despite this angled lead arrangement maintaining the board against guidebar 34, traditional planers still suffer from instability of the board as its passes through the planer. When the board is not well set against the guidebar 34 as it encounters the cutter heads 16 and 18, lateral movement of the board relative to guidebar 34 results and a defect known as a "snipe" wherein the cutter head digs excessively into the board surface and thereby downgrades the board. It is estimated that snipping of dimensioned lumber can downgrade as much as five to seven percent of a production run. As may be appreciated, five to seven percent downgrade of processed lumber can, over time, result in significant loss of overall product value.
To solve snipping problems in planers, prior designs have included holdover shoes or snipe shoes positioned as additional short guidebars creating lateral counter forces directly against the board forcing it to maintain contact with the guidebar 34 as the board passes the cutter heads 16 and 18. Unfortunately, force applied to the board as it moves rapidly through the planer results in frictional heat buildup, especially in the guidebar 34. As a result, guidebars have required water cooling systems to dissipate such heat energy and avoid the risk of fire in the planer machinery. Generally, prior planer designs have merely attempted to increase the lateral forces applied directly to the board to maintain the board stable against the guidebar 34 and thereby reduce the occurrence of snipping defects. Such additional snipping or holdover shoes add to the complexity of the machine and should not be considered a solution to the problem of snipping in a planer due to the associated frictional heat buildup.
Accordingly, it would be desirable to minimize the effect of snipping in a planer without including such excess apparatus, i.e., holdover shoes and snipping shoes, while still resolving the problem of stability of a board against a guidebar while the board moves rapidly through a planer. It would be further desirable to make more efficient the operation of a planer by minimizing operator effort required to accomplish such tasks as cutter head change over and correcting jammed or oversized wood articles.